Tantalum and niobium billets and methods of producing the same

ABSTRACT

Extruded tantalum billets and niobium billets are described having a substantially uniform grain size and preferably an average grain size of about 150 microns or less and more preferably an average grain size of about 100 microns or less. The extruded billet can then be forged or processed by other conventional techniques to form end use products such as sputtering targets. A process for making the extruded tantalum billets or niobium billets is also described and involves extruding a starting billet at a sufficient temperature and for a sufficient time to at least partially recrystallize the billet and form the extruded billet of the present invention.

[0001] This application claims the benefit under 35 U.S.C. § 119(e) ofprior U.S. Provisional Patent Application No. 60/261,001 filed Jan. 11,2001, which is incorporated in its entirety by reference herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to tantalum and niobium metals andmethods of forming products from tantalum and/or niobium, such astantalum billets or niobium billets. The present invention furtherrelates to tantalum billets or niobium billets that have a fine, uniformmicrostructure including a uniform grain size.

[0003] Metal billets, such as tantalum billets are commerciallyavailable from a variety of manufacturers. Typically, these billets aredefined by their minimum thickness and/or aspect ratio. Typical billetsare cylindrical in shape and have a diameter of 2 ½ inches or moreand/or have an aspect ratio of L/D of greater than 0.5. Thus, billetsare not metal plates or slabs and are typically an intermediate productformed from an ingot, such as a tantalum ingot. Tantalum billets arethen typically further processed by means such as forging into otherforms used by a variety of end users for such uses as sputtering targetsand the like. The tantalum billets provided to these end users typicallydo not have a fine and uniform grain size. Instead, commerciallyproduced tantalum billets have a grain structure that varies between thecenter and edge of the billet. The center of the commercial tantalumbillet typically has a microstructure composed of broad bands of larger,elongated grains adjacent to regions of varying fine grain size or ofunrecrystallized material. Conversely, the outer portions of thecommercial tantalum billets have a relatively fine and uniform grainstructure compared to the center of the billet. Thus, products forgedfrom billets having a coarse, non-uniform grain structure may alsoexhibit a coarse, non-uniform grain structure. For many high performanceapplications for tantalum such as sputtering targets and chemical energymunition warheads, a non-uniform grain structure has been reported todetrimentally impact product performance (S. I. Wright, G. T. Gray, andA. D. Rollett, Textural and Microstructural Gradient Effects on theMechanical Behavior of a Tantalum Plate, Metallurgical and MaterialsTransactions A, 25A, pp.1025-1031, 1994; C. A. Michaluk, R. O. Burt, andD. P. Lewis, Tantalum 101: Economics and Technology of Ta Materials,Semiconductor International, Vol. 23, No.8, pp.271-278, 2000; C. A.Michaluk, Correlating Discrete Orientation and Grain Size to the SputterDeposition Properties of Tantalum, Journal of Electronic Materials, Vol.31, No. 1, pp.2-9, 2002), all incorporated in their entirety byreference herein.

[0004] Accordingly, there is a need to provide tantalum and niobiumbillets having a uniform grain size and preferably made from high puritytantalum and/or niobium. In addition, there is a need to provide methodsto make such a tantalum billet or niobium billet.

SUMMARY OF THE PRESENT INVENTION

[0005] A feature of the present invention is to provide tantalum billetsor niobium billets having a substantially uniform grain size.

[0006] Another feature of the present invention is to provide methods tomake tantalum billets or niobium billets having a substantially uniformgrain size.

[0007] Another feature of the present invention is to provideintermediate billet products which can be used to form end use productssuch as sputtering targets wherein the end use products as well as theintermediate billet products have a substantially uniform grain size.

[0008] Additional features and advantages of the present invention willbe set forth in part in the description that follows, and in part willbe apparent from the description, or may be learned by practice of thepresent invention. The objectives and other advantages of the presentinvention will be realized and attained by means of the elements andcombinations particularly pointed out in the description and appendedclaims.

[0009] To achieve these and other advantages, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention relates to a tantalum billet having asubstantially uniform grain size. Preferably, the tantalum billet has anaverage grain size of about 150 microns or less. In addition, preferablythe purity of the tantalum in the billet is at least 99.95%. The billetof the present invention alternatively can be niobium with the samecharacteristics.

[0010] The present invention further relates to sputtering targetsformed from the above-described tantalum billets or niobium billets ofthe present invention.

[0011] Also, the present invention relates to a method of forming atantalum billet having substantially uniform grain size and involvestaking a tantalum ingot and cutting the ingot into large billets. Thelarge billets are either placed into a can which is then evacuated andsealed, or the billets are coated with a protective coating, whichprotects the large billets from oxidation during subsequent thermalprocessing and can also serve as a lubricant during subsequent extrusionoperations. The large billets are next heated at a sufficienttemperature to ensure at least the partial recrystallization of theextruded tantalum billet and preferably the full recrystallization ofthe tantalum billet. Afterwards, the can or protective coating can beremoved and the extruded rod, if desired, can be cut into smallerbillets or pieces and further processed by conventional methods, such asforging and the like. Again, the same steps can be used to form niobiumbillets.

[0012] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are intended to provide a further explanation ofthe present invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a flowchart showing a typical commercial processcompared to a preferred embodiment of the process of the presentinvention.

[0014] FIGS. 2(A) and 2(B) provide tables showing experimental resultsrelating to various parameters for certain materials made or used in theexamples of the present application.

[0015] FIGS. 3(A-B)-9(A-B) are photomicrographs showing the grainstructure of various samples used and/or prepared in the examples of thepresent application.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0016] The present invention relates to tantalum billets and/or niobiumbillets having a substantially uniform grain size. For purposes of thisinvention, billets are cylindrical in shape or can be shapes other thancircular cylinders such as forms having an oval, square, rectangular, orpolygonal cross-section. The present invention further relates toproducts formed from the tantalum billets and/or niobium billets such assputtering targets and the like. Also, the present invention relates tomethods of making the tantalum billets and niobium billets of thepresent invention.

[0017] With respect to the tantalum billet or the niobium billet,preferably, the billet has a substantially uniform grain size. Morepreferably, the billet has a uniform grain size throughout the diameterand length of the billet. For purposes of the present invention, asubstantially uniform grain size, measured in accordance to ASTM-E112,determined about any incremental area throughout the cross section ofthe extruded billet, does not deviate by more than about +/−100 micronsfrom the average ASTM grain size determined across the entire crosssection of the extruded billet. In addition, the size of the grainsabout the cross section of the extruded billet preferably vary uniformlyin accordance to a normal or Poissons distribution, and preferably doesnot exhibit a duplex microstructure as evident by a bimodal grain sizedistribution. Furthermore, the aspect ratio of the longitudinal grainspreferably does not exceed 20. Longitudinal grains are defined as thosecontained within any plane within the billet whose pole is perpendicularto the extrusion direction.

[0018] The extruded and annealed billet preferably exhibits a partiallyrecrystallized microstructure. More preferably, the billet is more than80% recrystallized, and most preferably the extruded billet is more than99% recrystrallized. The annealed billet, in addition, preferably has anaverage grain size of about 150 microns or less, though other grainsizes are within the bounds of the present invention. More preferably,the average grain size of the tantalum billet or the niobium billet ofthe present invention is about 150 microns or less and even morepreferably about 100 microns or less, and most preferably about 50microns or less. A preferred average grain size range is from about 25to about 150 microns and more preferably an average grain size range offrom about 25 microns to about 100 microns. The billets of the presentinvention preferably have a fine, uniform microstructure.

[0019] Preferably, the extruded billets of the present invention alsohave excellent texture characteristics, which are especially suitablefor such uses as sputtering targets.

[0020] The tantalum present in the tantalum billet preferably has apurity of at least 99.5% though other purities lower or higher than thiscan be used. More preferably, the tantalum metal has a purity of atleast 99.95% and can range in purity from about 99.5% to about 99.999%or more. Other ranges include from about 99.99% to about 99.995% andfrom about 99.995% to about 99.999% and from about 99.999% to about99.9995%. The tantalum that is present in the billet of the presentinvention can further include other metals and thus be a tantalum alloybillet which preferably comprises the high purity tantalum metal as oneof the components of the alloy. Other components which can form thetantalum alloy billet of the present invention include, but are notlimited to, yttrium, niobium, tungsten, molybdenum, titanium, silicon,halfnium, iron, nickel, chromium, and the like. The high purity tantalumthat can be used to form the tantalum billet of the present inventioncan be obtained following the procedures described in InternationalPublished Application No. WO 00/31310 which is incorporated herein inits entirety. Similar purity levels are preferred with niobium.

[0021] As described above, for purposes of the present invention, atantalum or niobium billet preferably has a cylindrical shape and has adiameter that is 2 ½ inches or greater. Another way to describe thebillet of the present invention is that the aspect ratio L/D is greaterthan 0.5 and preferably is 1.0 and more preferably is 2.0. The billet ofthe present invention in a preferred embodiment preferably has adiameter of from about 3 inches to about 5 inches and more preferablyfrom about 3 ½ inches to about 4 ½ inches, and even more preferablyabout 3 ⅞ inches with the billet having any height such as, but notlimited to, 5 to 7 inches.

[0022] As stated earlier, the billets of the present invention can thenbe subsequently formed into end use products such as sputtering targetsby cutting the billets into desired sizes and then upset forging thebillets into disks which can then be used as planar sputtering targets.In addition, the billets can be rolled to produce sheet or plate. Thebillets of the present invention can also be used for a variety of otheruses such as, but not limited to, hollow cathode magnetron (HCM)sputtering targets, chemical energy (CE) warhead liners, and feedstockfor deep-drawing applications such as cups, crucibles, and drawnseamless tubes, and the like.

[0023] Essentially, the billets of the present invention can be used inthe same manner as conventional tantalum and niobium billets except thebillets of the present invention have the improved properties withrespect to uniform grain size and preferably a small average grain size,such as about 150 microns or less which leads to a variety of desiredproperties such as, but not limited to, more homogeneous deformation andwork hardening throughout the workpiece during subsequent processing.This, in turn, allows for a reduction in the temperature of subsequentannealing operations and allows for the attainment of a finer, morehomogeneous microstructure in the final formed product than couldotherwise be realized by conventional processing.

[0024] The billets of the present invention are preferably made asfollows. Preferably, a tantalum ingot or niobium ingot is obtained andcut into large billet sizes such as from 6 to about 14 inches and morepreferably from about 8 to 11 inches in diameter and most preferablyabout ten inches in diameter with the length being any length. Examplesof suitable lengths include, but are not limited to, from about 10 toabout 40 inches and more preferably from about 15 to about 30 inches.This billet would be the starting billet size prior to converting thisbillet into the tantalum or niobium billet of the present invention.

[0025] Preferably, this starting billet is then either placed in a metalcan which can be evacuated and sealed, or the billet can be coated witha protective coating. The metal can or protective coating preferablyprevents the oxidation of the surface of the billet and acts as alubricant during the subsequent processing. Thus, any suitable can orprotective coating can be used as long it will prevent or reduceoxidation of the surface of the billet and will not deteriorate duringsubsequent processing steps. A suitable protective coating would be acopper coating which can be applied by conventional techniques such asflame spraying. Depending upon the extrusion temperatures discussedbelow, other protective coatings, such as glass-based coatings, may beemployed. At substantially high extrusion temperatures, a high meltingpoint metal can be used in combination with a glass coating. Forinstance, a metal can, such as molybdenum, can be used to protect thetantalum or niobium from contamination during soaking and extrudingoperations, while the glass coating provides lubrication. Followingextrusion, the glass particles are embedded in the inexpensive can metaland not in the tantalum or niobium billet. The glass contaminants canthen be removed by machining the can metal without having to machine theunderlying tantalum or niobium billet, resulting in an increased yieldof the more expensive tantalum or niobium material.

[0026] Once the can is in place or the protective coating is preferablyapplied, the starting billet can be heated at a sufficient temperatureand for a sufficient time to assure that the deformation and storedenergy is uniformly distributed in the workpiece during and afterextrusion, and preferably cause at least the partial dynamicrecrystallization and most preferably the full recrystallization of thebillet during extrusion. As an example, a conventional extruder can beused for extruding metals having a liner size equal to or greater thanthe length and diameter of the pre-extruded billet plus the can orprotective coating. As an example, an extrusion die fabricated fromhardened steel having a taper of about 45° and an inside diameter ofabout 4 inches can be used. The extrusion die set, prior to introductionof the starting billet can be generally heated to a temperature near thebillet soak temperature to prepare for extrusion. Suitable temperaturesinclude, but are not limited to, temperature ranges of from about 1200°F. to about 2950° F., and preferably about 1800° F.-1900° F. fortantalum. Once the billet is heated for a sufficient time so that thecenter of the billet is at or near the soak temperature, then thestarting billet can then be introduced into the extruder and extruded.

[0027] Typically, the extruder utilizes ram speeds of from about 0.1 toabout 10 inches/second, depending upon the capabilities of the extrusionmachine. In the preferred embodiment, if the starting billet has adiameter of about 10 inches, the extrusion preferably reduces thediameter of the billet to about 3 to 4 inches. The combination ofsoaking the billet at an elevated temperature and the subsequentadiabatic heating incurred during extrusion leads to the partialrecrystallization and preferably to the full recrystallization of thebillet. The resultant billet preferably contains a substantially uniformgrain size throughout the billet with a preferred average grain size ofabout 150 microns or less and more preferably an average grain size ofabout 100 microns or less. The billet can be produced by a single passthrough the extruder, or by a progression of extrusion operations, or bya combination of extrusion and conventional deformation processes.

[0028] After exiting the extruder, the extruded billet is preferablyallowed to air-cool, or optionally can be water-quenched to quicklyreduce the temperature of the extruded billet and prevent grain growth.In the preferred method, the can metal or protective coating can then beremoved by dissolving in acid, or machine cleaning, or any other type oftechnique used to remove coatings from metals.

[0029] Once the protective coating or can is removed, the extrudedbillet is preferably annealed to attain a partially recrystallizedmicrostructure, and most preferably to achieve a fully recrystallizedgrain structure with a homogenous or uniform grain size and preferablyan average grain size of 150 microns or less and more preferably under100 microns. The annealing can occur at any temperature to achievedesired levels of recrystallization, such as from about 950° C. or lessto about 1150° C. or more, and preferably occurs in a vacuum, such as atleast 1×10⁻⁴ Torr. The annealing time can be for 2 hours or othersuitable times, more than or less than 2 hours. The annealing processpreferably includes conventional acid pickling or other surface cleaningtechniques prior to annealing to remove any surface contaminants. Thebillet can then be cut into smaller pieces as described above andprocessed into end use products as with any type of conventionalbillets. For instance, the billet of the present invention can be forgedto a disk and used as a sputtering target. As stated earlier, with theextruded billet of the present invention having a substantially uniformgrain size as well as a fine grain size, the end use products formedfrom the billets have the same excellent properties which are beneficialfor the reasons stated earlier.

[0030] As an option or alternative embodiment, the extrusion of thebillets can occur in the manner described above but the extruded billetdoes not need to be at least partially recrystallized by the extrusionprocess. When recrystallization does not need to occur during theextrusion process, the extrusion can occur at any temperature such asfrom about ambient or room temperature (e.g., 20° C.-25° C.) totemperatures below the melting point of the tantalum or niobium.Preferably, the extrusion temperature is from about 1200° F. to about5400° F. for tantalum. If extrusion occurs with very littlerecrystallization occurring in the extruded billet or does not occur atall, the extruded billet can then be preferably subjected to one or moreannealing steps in order to cause at least partial, if not fullrecrystallization of the extruded billet. The annealing temperature is atemperature sufficient to cause at least partial recrystallization ofthe extruded billet and preferably full recrystallization of theextruded billet. Preferred annealing temperatures are from about 950° C.to about 1150° C. with respect to tantalum, for a preferred annealingtime of 2 hours. As indicated above, it is preferred to subject theextruded billet to conventional cleaning steps such as conventional acidpickling prior to any annealing to remove any surface contaminants.

[0031] The ingot which is used to form the billets of the presentinvention can be obtained by conventional techniques used to formtantalum or niobium ingots. For instance, the tantalum can be obtainedfrom ore and subsequently crushed and the tantalum separated from thecrushed ore through the use of an acid solution and a density separationof the acid solution containing the tantalum from the acid solutioncontaining niobium and other impurities. The acid solution containingthe tantalum can then be crystallized into a salt and this tantalumcontaining salt is then reacted with pure sodium in a vessel having anagitator typically constructed of nickel alloy material wherein the saltis then dissolved in water to obtain tantalum powder which can then bemelted by a variety of melting techniques such electron beam melting,vacuum arc remelting, or plasma melting.

[0032] Preferably, the starting ingot used to form the starting tantalumbillet is a high purity tantalum ingot. Generally, a process that can beused to make the high purity tantalum metal of the present inventioninvolves a refining process, a vacuum melting process, and a thermalmechanical process. In this process or operation, the refining processinvolves the steps of extracting tantalum metal preferably in the form apowder from ore containing tantalum and preferably the ore-containingtantalum selected has low amounts of impurities, especially, low amountsof niobium, molybdenum, and tungsten. More preferably, the amount ofniobium, molybdenum, and tungsten is below about 10 ppm, and mostpreferably is below about 8 ppm. Such a selection leads to a purertantalum metal. After the refining process, the vacuum melting processis used to purge low melting point impurities, such as alkydes andtransition metals from the tantalum while consolidating the tantalummaterial into a fully dense, malleable ingot. Then, after this process,the ingot can be mechanically worked, which helps to break-up theas-cast grain structure, to a size and form appropriate for extrusion.

[0033] The high purity tantalum metal preferably may be made by reactinga salt-containing tantalum with at least one agent (e.g., compound orelement) capable of reducing this salt to the tantalum metal and furtherresults in the formation of a second salt in a reaction container. Thereaction container can be any container typically used for the reactionof metals and should withstand high temperatures on the order of about800° C. to about 1,200° C. For purposes of the present invention, thereaction container or the liner in the reaction container, which comesin contact with the salt-containing tantalum and the agent capable ofreducing the salt to tantalum, is made from a material having the sameor higher vapor pressure as tantalum at the melting point of thetantalum. The agitator in the reaction container can be made of the samematerial or can be lined as well. The liner can exist only in theportions of the reaction container and agitator that come in contactwith the salt and tantalum. Examples of such metal materials which canform the liner or reaction container include, but are not limited to,metal-based materials made from nickel, chromium, iron, manganese,titanium, zirconium, hafnium, vanadium, ruthenium, cobalt, rhodium,palladium, platinum, or any combination thereof or alloy thereof as longas the alloy material has the same or higher vapor pressure as themelting point of tantalum metal. Preferably, the metal is a nickel or anickel-based alloy, a chromium or a chromium-based alloy, or an iron oran iron-based alloy. The liner, on the reaction container and/oragitator, if present, typically will have a thickness of from about 0.5cm to about 3 cm. Other thicknesses can be used. It is within the boundsof the present invention to have multiple layers of liners made of thesame or different metal materials described above.

[0034] The salt-containing tantalum can be any salt capable of havingtantalum contained therein such as a potassium-fluoride tantalum. Withrespect to the agent capable of reducing the salt to tantalum and asecond salt in the reaction container, the agent which is capable ofdoing this reduction is any agent which has the ability to result inreducing the salt-containing tantalum to just tantalum metal and otheringredients (e.g. salt(s)) which can be separated from the tantalummetal, for example, by dissolving the salts with water or other aqueoussources. Preferably, this agent is sodium. Other examples include, butare not limited to, lithium, magnesium, calcium, potassium, carbon,carbon monoxide, ionic hydrogen, and the like. Typically, the secondsalt which also is formed during the reduction of the salt-containingtantalum is sodium fluoride. Details of the reduction process which canbe applied to the present invention in view of the present applicationare set forth in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rdEdition, Vol. 22, pp. 541-564, U.S. Pat. Nos. 2,950,185; 3,829,310;4,149,876; and 3,767,456. Further details of the processing of tantalumcan be found in U.S. Pat. Nos. 5,234,491; 5,242,481; and 4,684,399. Allof these patents and publications are incorporated in their entirety byreference herein.

[0035] The above-described process can be included in a multi-stepprocess which can begin with low purity tantalum, such as ore-containingtantalum. One of the impurities that can be substantially present withthe tantalum is niobium. Other impurities at this stage are tungsten,silicon, calcium, iron, manganese, etc. In more detail, low puritytantalum can be purified by mixing the low purity tantalum which hastantalum and impurities with an acid solution. The low purity tantalum,if present as an ore, should first be crushed before being combined withan acid solution. The acid solution should be capable of dissolvingsubstantially all of the tantalum and impurities, especially when themixing is occurring at high temperatures.

[0036] Once the acid solution has had sufficient time to dissolvesubstantially all, if not all, of the solids containing the tantalum andimpurities, a liquid solid separation can occur which will generallyremove any of the undissolved impurities. The solution is furtherpurified by liquid-liquid extraction. Methyl isobutyl ketone (MIBK) canbe used to contact the tantalum rich solution, and deionized water canbe added to create a tantalum fraction. At this point, the amount ofniobium present in the liquid containing tantalum is generally belowabout 25 ppm.

[0037] Then, with the liquid containing at least tantalum, the liquid ispermitted to crystallize into a salt with the use of vats. Typically,this salt will be a potassium tantalum fluoride salt. More preferably,this salt is K₂TaF₇. This salt is then reacted with an agent capable ofreducing the salt into 1) tantalum and 2) a second salt as describedabove. This compound will typically be pure sodium and the reaction willoccur in a reaction container described above. As stated above, thesecond salt byproducts can be separated from the tantalum by dissolvingthe salt in an aqueous source and washing away the dissolved salt. Atthis stage, the purity of the tantalum is typically 99.50 to 99.99% Ta.

[0038] Once the tantalum powder is extracted from this reaction, anyimpurities remaining, including any contamination from the reactioncontainer, can be removed through melting of the tantalum powder.

[0039] The tantalum powder can be melted a number of ways such as avacuum arc remelt or an electron beam melting. Generally, the vacuumduring the melt will be sufficient to remove substantially any existingimpurities from the recovered tantalum so as to obtain high puritytantalum. Preferably, the melting occurs in a high vacuum such as 10⁻⁴torr or more. Preferably, the pressure above the melted tantalum islower than the vapor pressures of the metal impurities in order forthese impurities, such as nickel and iron to be vaporized. The diameterof the cast ingot should be as large as possible, preferably greaterthan 9 ½ inches. The large diameter assures a greater melt surface tovacuum interface which enhances purification rates. In addition, thelarge ingot diameter allows for a greater amount of cold work to beimparted to the metal during processing, which improves the attributesof the final products. Once the mass of melted tantalum consolidates,the ingot formed will have a purity of 99.995% or higher and preferably99.999% or higher. The electron beam processing preferably occurs at amelt rate of from about 300 to about 800 lbs. per hour using 20,000 to28,000 volts and 15 to 40 amps, and under a vacuum of from about 1×10⁻³to about 1×10⁻⁶ Torr. More preferably, the melt rate is from about 400to about 600 lbs. per hour using from 24,000 to 26,000 volts and 17 to36 amps, and under a vacuum of from about 1×10⁻⁴ to 1×10⁻⁵ Torr. Withrespect to the VAR processing, the melt rate is preferably of 500 to2,000 lbs. per hour using 25-45 volts and 12,000 to 22,000 amps under avacuum of 2×10⁻² to 1×10⁻⁴ Torr, and more preferably 800 to 1200 lbs.per hour at from 30 to 60 volts and 16,000 to 18,000 amps, and under avacuum of from 2×10⁻² to 1×10⁻⁴ Torr.

[0040] The resulting high purity metal ingot preferably has 10 ppm orless metallic impurities and preferably 50 ppm or less O2, 25 ppm orless N2, and 25 ppm or less carbon. If a purity level of about 99.995 isdesired, than the resulting high purity metal preferably has metallicimpurities of about 50 ppm or less, and preferably 50 ppm or less O2, 25ppm or less N2, and 25 ppm or less carbon. This ingot can then be usedin the manner described above to form the tantalum billets of thepresent invention.

[0041] As stated earlier, alternatively, niobium billets can be madefollowing the above-described extruding details. Accordingly, a niobiumbillet having a substantially uniform grain size is obtained. Thepreferred parameters for the grain size and other characteristics arethe same as for the tantalum parameters provided above, taking intoaccount the different melting temperature and other working conditionsof niobium (e.g., extruding at lower temperatures, such as from about1000° C. to about 1650° C.) that are known to those skilled in the art.

[0042] The present invention will be further clarified by the followingexamples, which are intended to be exemplary of the present invention.

EXAMPLES

[0043] Two tantalum production ingots produced by triple Electron Beam(3EB) melting were fabricated into 3.75″ diameter billets by differentprocessing methods. An ingot identified “Commercial Process” was a 12″diameter ingot weighing 3476 pounds. Chemistry results from samplestaken from the top, middle, and bottom of the ingot are provided inFIGS. 2(A) and 2(B). The ingot was manufactured into 3.75″ diameter rodusing standard commercial process shown in FIG. 1. A sample slice,approximately ½″ thick by machined diameter was cut from a billet takenfrom a position representing the middle portion of the forged product.The sample slice was annealed in a vacuum of at least 5×10⁻⁴ torr for 2hours. Metallographic specimens representing longitudinal cross-sectionsof the center and edge of the sample slice were polished in accordanceto standard metallographic procedures, and etched in a solution to50HF-50HNO₃ for 30-60 seconds. Results of the metallographic examinationof the commercially produced tantalum billet product are summarized inFIGS. 2(A) and 2(B).

[0044] An ingot of the present invention was a 10″ diameter ingotweighing 3734 pounds. Chemistry results from samples taken from the top,middle, and bottom sections of the ingot are also included in FIGS. 2(A)and 2(B), by reference to Φ and extrusion temperature. This second ingotwas cut into 4 sections approximately 20″ long and designated A, B, C,and D. Sections A-D were portioned from the bottom to the top of theingot, respectively, and hot extruded as described below and shown inFIGS. 1 and 2(A-B): Process A: Ingot Section A, Machined to 8.9″diameter, Canned in Copper, Soaked at 1800° F. for 6 hours, Extrudedfrom a 9.5″ liner through 4.0″ diameter die. Process B: Ingot Section B,Machined to 8.9″ diameter, Canned in Copper, Soaked at 1850° F. for 6hours, Extruded from a 9.5″ liner through 4.0″ diameter die. Process C:Ingot Section C, Machined to 8.9″ diameter, Canned in Copper, Soaked at1900° F. for 6 hours, Extruded from a 9.5″ liner through 4.0″ diameterdie. Process D: Ingot Section D, Machined to 9.5″ diameter, Canned inCopper, Soaked at 1900° F. for 6 hours, Extruded from a 10.25″ linerthrough 4.0″ diameter die.

[0045] Sample slices, each approximately ½″ thick by machined diameterwere cut from the center portion of each extruded rod. Each sample slidewas cut into wedges, and a wedge from each extruded rod was annealed ina vacuum of at least 5×10⁻⁴ torr for 2 hours at temperatures of 950,1050, and 1150° C. Metallographic specimens representing longitudinalcross-sections of the center and edge of the sample slice were polishedin accordance to standard metallographic procedures, then etched in asolution to 50HF-50HNO₃ for 30-60 seconds. Results of the metallographicexamination of the extruded tantalum billet products are included inFIGS. 2(A) and 2(B).

[0046] Photomicrographs showing the grain structure along thelongitudinal plane at the center and edge regions of the commerciallyproduced billet are shown in FIGS. 3(A) and 3(B). Here, the billet axisis perpendicular to the micron scale on the images. FIGS. 3(A) and 3(B)show many of the issues associated with the microstructure ofcommercially produced tantalum billet. First, the center of the billetcontains a duplex grain structure comprised of broad bands ofunrecrystallized material containing small islands of crystallitesadjacent to regions containing large, elongated grains. The center ofthe commercial billet exhibited a grain size range from about 20 toabout 245 μm., the largest range of grain size observed in all materialsexamined. Second, the grain structure character along the edge of thecommercial billet was fully recrystallized and relatively uniform. Thiswas significantly different than that in the center of the billet, andreflected the microstructural inhomogeneity seen in commerciallyproduced tantalum billets.

[0047] Photomicrographs showing the center and edge section of extrudedrod A, annealed at 950, 1050, and 1150° C., are provided in FIGS. 4(A)and 4(B), 5(A) and 5(B), and 6(A) and 6(B), respectively. Comparing theimages in FIGS. 4-6 demonstrate the general effect of annealingtemperature on the microstructure. The grain size character seen inFIGS. 4(A) and 4(B) were similar to that observed in the commercialbillet, but with noticeably lesser amount of duplexing. In general,increasing the annealing temperature from 950 to 1050° C. did notdramatically increase the average grain size of the extruded tantalumbillets, but did enhance grain size uniformity and percentrecrystallization. An anneal temperature of 1150° C. did promote somegrain growth without sacrificing uniformity in the extruded tantalumbillets. The higher temperature anneal assured that the microstructurethroughout the extruded tantalum billet was uniform and fullyrecrystallized.

[0048] Photomicrographs of the center and edge regions of extrudedbillets A, B, C, and D, each annealed at 1150° C. for 2 hours, are givenin FIGS. 6(A) and (B), 7(A) and (B), 8(A) and (B), and 9(A) and (B),respectively. Together, FIGS. 6-9 reveal the influence of extrusiontemperature and billet size on the grain structure of the extrudedtantalum billet. For the 8.9″ diameter ingot sections extruded from a9.5″ diameter liner and annealed at 1150° C. for 2 hours, increasing theextrusion temperature from 1800 to 1900° F. had a slight effect onincreasing the grain size and enhancing grain size uniformity. Thistrend shows that increasing the extrusion temperature increases theuniformity of deformation and stored energy in the material impartedduring extrusion. However, for a 1900° F. extrusion temperature,increasing the diameter of the ingot section from 8.9 to 9.5″ andextrusion liner from 9.5 to 10.25″ diameter produced a billet producthaving an equal or finer average grain size and similar grain sizeuniformity. This observation demonstrates that increasing thepre-extruded ingot diameter allows for a greater amount of stored energyto be imparted to the extruded billet.

[0049] Together, the information developed in this example concludesthat the optimum process involves extruding large 9.5″ diameter tantalumingot sections at a temperature of 1900° F. to produce a 4″ diameteras-extruded rod that can machined into 3.75″ diameter billets. A fullyrecrystallized and relatively uniform microstructure having an averagegrain size below 100 μm across the entire cross section of the billet isachieved after annealing the extruded tantalum billet at a temperatureof 1050-1150° C.

[0050] Other embodiments of the present invention will be apparent tothose skilled in the art from consideration of the present specificationand practice of the present invention disclosed herein. It is intendedthat the present specification and examples be considered as exemplaryonly with a true scope and spirit of the invention being indicated bythe following claims and equivalents thereof.

What is claimed is:
 1. A tantalum billet having a substantially uniform grain size.
 2. An extruded tantalum billet having a substantially uniform average grain size.
 3. The extruded tantalum billet of claim 2, wherein said average grain size is about 150 microns or less.
 4. The extruded tantalum billet of claim 2, wherein said average grain size is about 100 microns or less.
 5. The extruded tantalum billet of claim 2, wherein said average grain size is about 50 microns or less.
 6. The extruded tantalum billet of claim 2, wherein said average grain size is from about 25 microns to about 100 microns.
 7. The extruded tantalum billet of claim 2, having a purity of at least about 99.995%.
 8. The extruded tantalum billet of claim 2, wherein said tantalum billet is fully recrystallized.
 9. The extruded tantalum billet of claim 2, wherein said tantalum billet is at least partially recrystallized.
 10. The extruded tantalum billet of claim 2, wherein said tantalum billet is about 98% or more recrystallized.
 11. The extruded tantalum billet of claim 2, wherein said tantalum billet is about 80% or more recrystallized.
 12. The extruded tantalum billet of claim 2, having a purity of from about 99.995% to about 99.999%
 13. The extruded tantalum billet of claim 2, further comprising at least one alloy material.
 14. A sputtering target comprising the extruded tantalum billet of claim
 2. 15. A capacitor can comprising the extruded tantalum billet of claim
 2. 16. A resistive film layer comprising the extruded tantalum billet of claim
 2. 17. An article comprising at least as a component the extruded tantalum billet of claim
 2. 18. A process for making the extruded tantalum billet of claim 2 comprising extruding a tantalum ingot at a sufficient temperature and for a sufficient time to at least partially recrystallize the tantalum billet during extrusion.
 19. The process of claim 18, wherein said sufficient temperature is from about 1200° F. to about 2950° F.
 20. The process of claim 18, wherein said temperature is uniform throughout the extrusion process.
 21. The process of claim 18, further comprising the step of water quenching the extruded tantalum billet after extrusion.
 22. The process of claim 18, further comprising machine cleaning the extruded tantalum billet.
 23. A process for making the extruded tantalum billet of claim 2, comprising extruding a starting tantalum billet at a sufficient temperature and for a sufficient time to at least partially recrystallize the tantalum billet to form said extruded tantalum billet.
 24. The process of claim 23, wherein said sufficient temperature is from about 1200° F. to about 2950° F.
 25. The process of claim 23, wherein said temperature is uniform throughout the extrusion process.
 26. The process of claim 23, further comprising the step of water quenching the extruded tantalum billet after extrusion.
 27. The process of claim 23, further comprising machine cleaning the extruded tantalum billet.
 28. A process for making the extruded tantalum billet of claim 2, comprising cutting an ingot into at least one starting billet and either applying a protective coating on said starting billet or placing said starting billet in a can; extruding the starting billet at a sufficient temperature and for a sufficient time to at least partially recrystallize the tantalum billet and to form said extruded tantalum billet.
 29. The process of claim 28, wherein said sufficient temperature is from about 1200° F. to about 2950° F.
 30. The process of claim 28, wherein said temperature is uniform throughout the extrusion process.
 31. The process of claim 28, further comprising the step of water quenching the extruded tantalum billet after extrusion.
 32. The process of claim 28, further comprising machine cleaning the extruded tantalum billet.
 33. The process of claim 28, wherein said ingot is obtained by the electron beam melting of a high purity tantalum powder feedstock.
 34. The process of claim 28, wherein said protective coating or can is removed after said extruding.
 35. The process of claim 34, wherein said protective coating is removed by acid washing or machine cleaning, or both.
 36. A niobium billet having a substantially uniform grain size.
 37. An extruded niobium billet having a substantially uniform average grain size.
 38. The extruded niobium billet of claim 37, wherein said average grain size is about 150 microns or less.
 39. The extruded niobium billet of claim 37, wherein said average grain size is about 100 microns or less.
 40. The extruded niobium billet of claim 37, wherein said average grain size is about 50 microns or less.
 41. The extruded niobium billet of claim 37, wherein said average grain size is from about 25 microns to about 100 microns.
 42. The extruded niobium billet of claim 37, having a purity of at least about 99.995%.
 43. The extruded niobium billet of claim 37, wherein said niobium billet is fully recrystallized.
 44. The extruded niobium billet of claim 37, wherein said niobium billet is at least partially recrystallized.
 45. The extruded niobium billet of claim 37, wherein said niobium billet is about 98% or more recrystallized.
 46. The extruded niobium billet of claim 37, wherein said niobium billet is about 80% or more recrystallized.
 47. The extruded niobium billet of claim 37, having a purity of from about 99.995% to about 99.999%
 48. The extruded niobium billet of claim 37, further comprising at least one alloy material.
 49. A sputtering target comprising the extruded niobium billet of claim
 37. 50. A capacitor can comprising the extruded niobium billet of claim
 37. 51. A resistive film layer comprising the extruded niobium billet of claim
 37. 52. An article comprising at least as a component the extruded niobium billet of claim
 37. 53. A process for making the extruded niobium billet of claim 37 comprising extruding a niobium ingot at a sufficient temperature and for a sufficient time to at least partially recrystallize the niobium billet during extrusion.
 54. The process of claim 53, wherein said sufficient temperature is from about 1000° F. to about 2650° F.
 55. The process of claim 53, wherein said temperature is uniform throughout the extrusion process.
 56. The process of claim 53, further comprising the step of water quenching the extruded niobium billet after extrusion.
 57. The process of claim 53, further comprising machine cleaning the extruded niobium billet.
 58. A process for making the extruded niobium billet of claim 37, comprising extruding a starting niobium billet at a sufficient temperature and for a sufficient time to at least partially recrystallize the niobium billet to form said extruded niobium billet.
 59. The process of claim 58, wherein said sufficient temperature is from about 1000° F. to about 2650° F.
 60. The process of claim 58, wherein said temperature is uniform throughout the extrusion process.
 61. The process of claim 58, further comprising the step of water quenching the extruded niobium billet after extrusion.
 62. The process of claim 58, further comprising machine cleaning the extruded niobium billet.
 63. A process for making the extruded niobium billet of claim 37, comprising cutting an ingot into at least one starting billet and either applying a protective coating on said starting billet or placing said starting billet in a can; extruding the starting billet at a sufficient temperature and for a sufficient time to at least partially recrystallize the niobium billet and to form said extruded niobium billet.
 64. The process of claim 63, wherein said sufficient temperature is from about 1000° F. to about 2650° C.
 65. The process of claim 63, wherein said temperature is uniform throughout the extrusion process.
 66. The process of claim 63, further comprising the step of water quenching the extruded niobium billet after extrusion.
 67. The process of claim 63, further comprising machine cleaning the extruded niobium billet.
 68. The process of claim 63, wherein said ingot is obtained by the electron beam melting of a high purity niobium powder feedstock.
 69. The process of claim 63, wherein said protective coating or can is removed after said extruding.
 70. The process of claim 69, wherein said protective coating is removed by acid washing or machine cleaning, or both.
 71. The process of claim 18, further comprising annealing said extruded tantalum billet.
 72. The process of claim 71, wherein said annealing occurs at a temperature and for a time sufficient to at least partially recrystallize the extruded tantalum billet during annealing.
 73. The process of claim 71, wherein said annealing occurs at a temperature of from about 950° C. to about 1150° C. for about 2 hours.
 74. The process of claim 23, further comprising annealing said extruded tantalum billet.
 75. The process of claim 74, wherein said annealing occurs at a temperature and for a time sufficient to at least partially recrystallize the extruded tantalum billet during annealing.
 76. The process of claim 74, wherein said annealing occurs at a temperature of from about 950° C. to about 1150° C. for about 2 hours.
 77. The process of claim 28, further comprising annealing said extruded tantalum billet.
 78. The process of claim 77, wherein said annealing occurs at a temperature and for a time sufficient to at least partially recrystallize the extruded tantalum billet during annealing.
 79. The process of claim 77, wherein said annealing occurs at a temperature of from about 950° C. to about 1150° C. for about 2 hours.
 80. The process of claim 53, further comprising annealing said extruded niobium billet.
 81. The process of claim 80, wherein said annealing occurs at a temperature and for a time sufficient to at least partially recrystallize the extruded niobium billet during annealing.
 82. The process of claim 80, wherein said annealing occurs at a temperature of from about 950° C. to about 1150° C. for about 2 hours.
 83. The process of claim 58, further comprising annealing said extruded niobium billet.
 84. The process of claim 83, wherein said annealing occurs at a temperature and for a time sufficient to at least partially recrystallize the extruded niobium billet during annealing.
 85. The process of claim 83, wherein said annealing occurs at a temperature of from about 950° C. to about 1150° C. for about 2 hours.
 86. The process of claim 63, further comprising annealing said extruded niobium billet.
 87. The process of claim 86, wherein said annealing occurs at a temperature and for a time sufficient to at least partially recrystallize the extruded niobium billet during annealing.
 88. The process of claim 86, wherein said annealing occurs at a temperature of from about 950° C. to about 1150° C. for about 2 hours.
 89. A process for making the extruded tantalum billet of claim 2, comprising extruding a tantalum ingot to form an extruded tantalum billet and then annealing said extruded tantalum billet at a sufficient temperature and for a sufficient time to at least partially recrystallize the extruded tantalum billet.
 90. A process for making the extruded tantalum billet of claim 2, comprising extruding a starting tantalum billet to form said extruded tantalum billet and then annealing said extruded tantalum billet for a sufficient time and for a sufficient temperature to at least partially recrystallize the extruded tantalum billet.
 91. A process for making the extruded tantalum billet of claim 2, comprising cutting an ingot into at least one starting billet and either applying a protective coating on said starting billet or placing said starting billet in a can; extruding the starting billet to form said extruded tantalum billet and then annealing said extruded tantalum billet at a sufficient temperature and for a sufficient time to at least partially recrystallize the extruded tantalum billet.
 92. A process for making the extruded niobium billet of claim 37, comprising extruding a niobium ingot to form an extruded niobium billet and then annealing said extruded niobium billet at a sufficient temperature and for a sufficient time to at least partially recrystallize the extruded niobium billet.
 93. A process for making the extruded niobium billet of claim 37, comprising extruding a starting niobium billet to form said extruded niobium billet and then annealing said extruded niobium billet for a sufficient time and for a sufficient temperature to at least partially recrystallize the extruded niobium billet.
 94. A process for making the extruded niobium billet of claim 37, comprising cutting an ingot into at least one starting billet and either applying a protective coating on said starting billet or placing said starting billet in a can; extruding the starting billet to form said extruded niobium billet and then annealing said extruded niobium billet at a sufficient temperature and for a sufficient time to at least partially recrystallize the extruded niobium billet. 